Optical communication, also known as optical telecommunication, is communication at a distance using light to carry information. An optical communication system uses a transmitter to encode a message in an optical signal, a channel to carry the signal to its destination, and a receiver to reproduce the message from the received optical signal.
An optical fiber is the most common type of channel for optical communications. The transmitters in optical fiber communications are typically laser diodes. Infrared light or visible light can be used, although infrared light is more commonly used because it is transmitted through optical fibers with less attenuation and dispersion than visible light. The signal encoding is typically simple intensity modulation, although optical phase and frequency modulation are also possible.
As explained in further detail below, natural variations in operating conditions affect the optical power output of laser diodes. As shown in FIG. 1, a conventional transmitter 100 uses a top-side coupled photodiode 102 to detect the intensity of laser backlight (light emitted from the back facet of a laser diode 104) as a feedback signal to monitor and control the optical output power. The conventional packaging approach positions photodiode 102 in an L-shaped configuration with respect to laser diode 104 so that light emitted from laser diode 104 is incident on a top-side of photodiode 102. One problem with this approach is that it requires a bulky and expensive “wrap-around” sub-mount 106.